[SCTP] Fix sctp_get{pl}addrs() API to work with 32-bit apps on 64-bit kernels.

The old socket options are marked with a _OLD suffix so that the
existing 32-bit apps on 32-bit kernels do not break.

Signed-off-by: Ivan Skytte Jørgensen <isj-sctp@i1.dk>
Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>